Electroplating process



June 30, 1942. R. A. HOFFMAN 2,238,318

ELECTROPLATING PROCESS Filed Dec. 29, 1937 Raymond A. Haf/nmn INVENTOR A TTORNEY Patented June 30, 1942 2,288,318 ELECTROPLATIYNG raocsss Raymond A. Hoffman, Euclid, Ohio, assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application December 29, 1937, Serial No. 182,219

12 Claims.

This invention relates to the electrodeposition of zinc, and is particularly directed to processes and plating solutions wherein a bright, mirrorlike zinc deposit is plated from a cyanide-zinc bath which contains as an organic addition agent a soluble phenol-aldehyde condensation product.

The phenol-aldehyde condensation products which serve as addition agents for cyanide-zinc plating baths according to my invention may suitably be prepared by reacting any phenol with any aldehyde to produce a condensation product soluble in a cyanide zinc plating bath. I have found it satisfactory to form the organic addition agents of my invention by the reaction of a phenol selected from the group consisting of catechol,

cresol, hydroxy diphenyl, naphthol, and phenol crotonaldehyde, formaldehyde, i'urfural, paralde-.

hyde, and propionaldehyde.

The phenol-aldehyde condensation products should be prepared under such conditions of concentration, temperature and reaction rate that the products obtained are soluble in a cyanidezinc plating bath. Phenol-aldehyde condensation products are of course well-known in the art as such, and it is already well understood how to control their formation to produce products of desired solubility.

It will be understood that when reference is made herein to the phenol-aldehyde condensation products being soluble in a cyanide-zinc plating bath, it is meant that they are adequately soluble to serve as addition agents. The com pounds may be very difiicultly soluble, but if some of the addition agent dissolves, the dissolved material even tho present in exceedingly small amounts effects an improvement in the character of a zinc deposit.

Phenol-aldehyde condensation products which are difficultly soluble may more easily be put in the solution by first dissolving the condensation product in a solvent such as alcohol or acetone and then adding the addition agent to the bath in such solvent.

It may also be found desirable sometimes to aid solution of phenol-aldehyde condensation products according to my invention by the joint use of a protective colloid. It is further to be observed that when a protective colloid is used, the combination of addition agents facilitates the initial formation of a zinc deposit. As a protective colloid suitable for use with phenol-aldehyde I may mention gelatin, gum arabic, gum tragacanth, agar-agar, and soluble starch.

The soluble phenol-aldehyde condensation products of my invention may also be used with advantage in combination with metal brighteners in cyanide-zinc plating baths such as those shown in the Westbrook Patent 2,080,520 and the Hofl Patent 2,080,479. Metal brighteners for use with the addition agents of my invention may be a soluble compound of a metal of the group consisting of molybdenum, chromium, cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

The addition agents of my invention have been used in various baths and the deposits obtained examined by means of a reflectometer which measures the amount of light reflected by the coatings and permits a quantitative statement as to the brilliance of the deposit.

The refiectometer, which is illustrated in the drawing, is similar to instruments heretofore used in the study of enameled surfaces, paint films, and the like.

In the drawing, l designates a box having a cover 2 and divided by a central partition 1. In one side of the box there is provided a light source 3, a fifty candlepower automobile headlight bulb. To furnish current to the bulb, a storage battery is used, the current being regulated by the use of a rheostat so that about three volts are supplied to the lamp.

Below the bulb there is provided a concave mirror 4 which serves to intensify the light to some extent. This concave mirror is about three 5 inches below the bulb.

condensation products according to my invention Above the light bulb there is a black partition 5 provided with a one-half inch by one inch slit. The bulb is about three and one-half inches from the specimen being tested.

Light from the bulb 3 passes thru the slit 6 and is reflected by the specimen to the selenium photoelectric cell 9. The photoelectric cell is on a slight incline, being supported by the member 8. The cell is about five and one-half inches from the specimen.

The photoelectric cell is connected to a microammeter III which shows directly the number of microamperes generated by the cell in response to the light reflected by the specimen.

The top 2 of the box I has a slit il therein thru which light can pass. A metal plate I 2 is set over the hole, the plate having a. one-quarter by three-quarter inch rectangular slit. On top of the box and covering the metal plate there is positioned a chamois skin ll upon which specimen plates may be placed without danger of scratching. The chamois is provided with an opening registering with the slit I 3.

Before starting to use the reflectometer, it was calibrated with a standard reflecting surface. A silver mirror was made by plating a polished copper sheet with silver and then bufflng. The mirror was placed face down on the chamois over the slit. The current supplied to the bulb 3 was then adjusted until the microammeter read 49.

In view of the fact that a silver mirror quickly loses its maximum brilliance, and in view of the difficulty of preparing new silver mirrors, a less changeable secondary standard was established. A silvered glass mirror was placed face down over the slit l3 and its position so marked that the same surface could be found when desired. The glass mirror gave a reading of 45 microamperes.

Each time that the reflectometer was used, it was recalibrated with the glass mirror. This is necessary because with the same applied current the bulb gives varying amounts of light depending upon its temperature and upon other variables. At frequent intervals a new polished silver mirror was prepared in accordance with the best practice and used to recheck the glass mirror .so that 'when the silver mirror read 49 microamperes, a portion of the glass mirror reading 45 microamperes would be used as standard.

When no specimen is placed on top of the refiectometer, a reading of less than one microampere is obtained. This reading represents the error by reason of light leaking to the photoelece tric cell. 3

In the following examples, unless otherwise stated, specimens were plated on polished copper sheets at current densities from five to one hundred and fifty amperes per square foot. Specimens plated at current densities of about seven, twenty-five, forty, and eight amperes per square foot were placed on the refiectometer for brightness determinations.

So that the results would be comparable, the deposits were made on copper plates polished so that on the reflectometer, readings of 30 "to 35 would be obtained over the whole surface. When plates diil'ering as much as 5 microamperes were zinc plated under the same conditions and from the same bath, the zinc deposits differed by only about one microampere or less.

While most commercial zinc plating is not done on polished surfaces, the deposits obtained on polished copper sheets are nonetheless significant.

- A bath which produces a dull deposit on a polished surface will produce a dull and poor deposit on, a matte surface, while a bath which produces a bright deposit on a polished surface will produce -a correspondingly better deposit on a matte surface. The deposits obtained on polished Grams per liter Zinc cyanide (Zn(CN)z) 60 Sodium hydroxide (NaOH) '78 Sodium cyanide (NaCN) 42 At the time the bath was made up, two and fivetenths grams per liter of zinc dust was added together with the bath constituents. The zinc dust eifecteda removal of deleterious impurities from the bath.

In the following examples the effect of a brightdip was observed by subjecting the deposits to the action of a one-fourth per cent solution of nitric acid for about fifteen seconds.

Example 1 Current density (amps.

per sq. ft.) 7 25 40 Not bright-dipped 12 13 12 12 Av. 12.3

Bright-dipped 20 28 26 28 Av. 25.5

The deposits were of excellent character. When the bath above described was used to plate various steel stampings and other such articles, zinc deposits of excellent character and uniformity were obtained.

It is to be observed that unlike most organic addition agents, the phenol-aldehyde addition agents of my invention exercise their most marked influence at high current densities. This unusual behavior of the addition agents of my invention make them particularly well adapted for use in solutions for still-plating installations.

The cresol-acetaldolreaction product of this example may be used in widely varying concentrations to the extent of its rather limited solubility. The best results were obtained using seven grams per liter as indicated.

A similar plating 'bath was made up using seven grams per liter of the cresol-acetaldol condensation product of this example together with eight grams per liter of molybdenum trioxide (M003). Zinc was deposited on a number of polished copper sheets and the deposit brightness determined with the following results:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 21 30 3'7 38 Bright-dipped 31 36 41 512 Current density (amps. per sq.

'1 25 40 80 Not bright-dipped 15 15 4 7 Brightdipped 30 30 19 17 For further purposes of comparison, a cyanidezinc plating bath was made up with eight grams per liter of molybdenum trioxide but omitting the phenol resin. The following brilliance readings were obtained on deposits produced in this bath:

Current density (amps. per sq.

7 25 40 80 Not bright-dipped 22 30 30 Bright-dipped 28 30 33 30 Example 2 I Current density (amps.

per sq. ft.) 7 40 80 I Not bright-dipped 9 24 2'7 25 Av. 21.3 Bright-dipped 19 31 31 Av. 27.8

A cyanide-zinc plating bath was made up using the catechol-acetaldol condensation products of this example to the extent of nine gramsper liter together with eight grams .per liter of molybdenum trioxide (M003) as a metal brightener. Brilliant zinc deposits were obtained with this bath. The brilliance of deposits on polished cop'- per sheets was as follows:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 13 22 33 35 Bright-dipped 25 31 39 42 I Example 3 A cyanide-zinc plating bath was made up using a cresol-acetaldol condensation product quite similar to that of Example 1. The condensation product was prepared by reacting equimolecular quantities of para-cresol and acetaldol at a temperature of 110 C. The material was 'a black liquid which did not entirely dissolve in the bath, a portion of the condensation product forming a sticky residue which floated on the bath surface. While this addition agent was considerably less soluble than that of Example 1, it was still moderately soluble and the best results were obtained using seven grams per liter of this addition agent.

Zinc deposits made using the cresol-acetalol condensation product of this example to the amount of seven grams per liter in a cyanidezinc plating bath gave zinc deposits of very satisfactory character. The following reflectometer readings were obtained:

Current density (amps. per sq.

ft.) 7 25 80 Not bright-dipped 10 20 30 27 Bright-dipped 27 31 35 37 Current density (amps. per sq.

7 25 40 80 Not bright-dipped 16 21 35 31 Bright-dipped 28 28 39 37 Example 4 A cyanide-zinc plating bath was made up using three grams per liter of an organic addition agent prepared by reacting equimolecular quantities of para-cresol and crotonaldehyde. A small amount of foaming was observed during electrolysis of the bath so prepared. Zinc deposits produced using this bath gave the following reflectometer data:

Current density (amps. per sq.

Not bright-dipped 16 ll ll 13 Bright-dipped 24 28 28 27 A similar cyanide-zinc plating bath was made up using three grams per liter of the cresolcrotonaldehyde condensation product and eight grams per liter of molybdenum trioxide. Zinc deposits of excellent character were obtained and specimen plates gave the following reflectometer readings:

Current density (amps. per sq.

7 25 40 80 Not bright-dipped 14 27 30 25 Bright-dipped 30 34 33 36 Example 5 A cyanide-zinc plating bath was made up using an organic addition agent prepared by reacting equimolecular quantities of ortho-cresol and crotonaldehyde. Six grams per liter of the organic addition agent gave the best results and when a bath was made up using this quantity of addition agent, the following reflectometer readings were obtained:

Current density (amps. per sq.

7 25 40 80 Not bright-dipped 16 13 l3 l3 Bright-dipped 23 25 29 28 A bath made up as above and containing additionally eight grams per liter of molybdenum trioxide gave deposits of excellent character. With specimen zinc plates the following reflectometer readings were obtained:

Current density (amps. per sq.

ft.) Not bright-dipped 17 20 34 36 Bright-dipped 29 28 36 36 Example 6 grams per liter of this cresol-acetaldol conden-' sation product, the following reflectometer readings being obtained:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 15 25 26 23 Bright-dipped 32 37 37 36 A cyanide-zinc plating bath similarly constituted but containing in addition eight grams per liter of molybdenum trioxide gave zinc deposits of excellent character. Specimen plates on polished copper sheets had the indicated brightness at the indicated current densities:

Current density (amps. per sq.

a.) v 25 40 so Not bright-dipped -16 13 ea s'z Bright-dipped 2o 25 42 39 Example 7 A'cyanide-zinc plating bath was made up using as an addition agent a condensation product prepared by reacting equimolecular quantities of lpara hydroxydiphenyl and acetaldol. The hydroxydiphenyl-acetaldol condensation product is a white solid soluble to the extent of about one gram per liter. Using this addition agent at its maximum concentration in the bath deposits of very good character were obtained and specimen plates gave the following data:

Current density (amps. per sq.

ft.) 7 '25 4o 80 Not bright-dipped 12 17 18 Bright-dipped 26 34 35 34 A similar cyanide-zinc plating bath was made up including additionally eight grams per liter of molybdenum trioxide. The deposits thus obtained before bright-dipping were much better than ones produced without the use of molybdenum, but bright-dipped deposits did not seem to be much benefited by the use of molybdenum. With specimen deposits on polished copper sheets the following refiectometer readings were obtained with the bath using both the hydroxydiphenyl-acetaldol condensation products and molybdenum trioxide:

Current density (amps. per sq.

Not bright-dipped 8 25 29 37 Bright-dipped 25 34 34 33 Example 8 A cyanide-zinc plating bath was made up including as an organic addition-agent the condensation product prepared by reacting equimolecular quantities of para-hydroxydiphenyl and furfural. The condensation product was most effective at a concentration of seven grams per liter. Considerable foam was formed on the bath during passage of current. With this bath the following brightness data was obtained:

Current density (amps. per sq.

1 7 25 40 80 Not bright-dipped 12 15 17 21 Bright-dipped 19 31 32 29 A -similar cyanide-zinc plating bath was made up using seven grams per liter :of the para-hydroxydiphenyl-furfural condensation product, together with eight grams per liten-of molybdenum trioxide. Specimen zinc electrodeposits on pol- ?ished copper sheets gave the following brightness zrefl d nlli Current density (amps. per sq.

"7 25 '40 80 Notibright-dipped 30 31 33 29 Bright-dipped 25 34 36 so Example 9 A cyanide-zinc plating bath was made up using as an organic addition agent a condensation product prepared by reacting para-hydroxydiphenyl with an excess of propionaldehyde at 70 C. The condensation product was used in the bath up to five grams per liter. This quantity amounts to the limit of solubility of the condensation product since not all of the five grams per liter added dissolved, whereas smaller amounts were completely dissolved. With a bath to which had been added five grams per liter of the condensation product specimen zinc deposits gave the following brightness data:

Current density (amps. per sq.

ft.) 7 25 40 Not bright-dipped 17 11 11 10 Bright-dipped 28 22 22 20 A cyanide-zinc plating bath was similarly made up using five grams per liter of the hydroxydiphenylpropionaldehyde condensation product, together with eight grams per liter of molybdenum trioxide. Zinc electro-deposits obtained from this bath gave the [following brilliance readings:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 15 25 26 25 Bright-dipped 23 31 33 31 Example 10 A cyanide-zinc plating bath was made up using as an addition agent five grams per liter'of a condensation product prepared by reacting betanaphthol with an excess of acetaldehyde at 61 C. There was a considerable amount of foaming of the bath during passage of current. With this bath zinc deposits were obtained having the following brightness characteristics at the indicated current densities:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dippeiL", 13 10 13 18 Bright-dipped ..1. 27 25 '30 30 Asimilarbath was made up using additionally eight {grams per liter of molybdenum trioxide and with (this bath the following brilliance data was obtained:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright dipped 13 1-7 25 23 Bright-dipped .23 28 34 34 Example 11 A cyanide-zinc bath was made up using three grams :per liter ofa phenol-aldehyde condensation product prepared by reacting equimolecular (quantities of metacresol and crotonaldehyde. A :slight foaming of the bath was noticeable during passage of current. With this bath specimen zinc plates on polished copper sheets gave the following brightness data:

A cyanide-zinc plating bath was made up using three grams per liter of a condensation product prepared by reacting phenol, paraldehyde, and

formaldehyde at 85 C. for one-half hour. About three grams per liter seems to be as much 01' the condensation product as could be dissolved in a bath. With this bath zinc electrodeposits were obtained which gave the following brightness readings:

Current density (amps. per sq.

7 25 40 so Not bright-dipped 10 1o 12 13 Bright-dipped. 24 2s 29 29 Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 12 22 18 Bright-dipped 29 31 32 Example 13 A cyanide-zinc plating bath was made up using as an organic addition agent the reaction product of catechol with an excess of formaldehyde. The condensation product was used in as great an amount as could be dissolved in the bath which seems to'be about 0.5 gram per liter. With this bath there were obtained zinc electrodeposits with the following brilliance readings:

Current density (amps. per sq.

7 25 40 80 Not bright-dipped 12 21 22 23 Bright-dipped 23 30 31 Example 14 A cyanide-zinc plating bath was made up using seven grams per liter of a condensation product prepared by reacting equimolecular quantities of catechol and paraldehyde. Very slight foaming of the bath was noted during passage of current. With this bath zinc electrodeposits were obtained which had the following brightness:

Current density (amps. per sq.

ft.) 7 25 40 80 Not bright-dipped 12 19 16 17 Bright-dipped 20 30 30 30 A similar cyanide-zinc plating bath was made up including both the catechol-paraldehyde condensation product and eight grams per liter of molybdenum trioxide. With this bath zinc deposits were obtained as follows:

Current density (amps. per sq. ft.) 7 25 40 80 Not bright-dipped 17 18 26 13 Bright-dipped 30 28 20 Example 15 A cyanide-zinc plating bath was made up with an organic addition agent prepared by reacting equimolecular quantities of catechol and butyraldehyde, the organic addition agent being used at a concentration of about five grams per liter in which amount it exercised its optimum eifect. The bath foamed slightly during electrolysis. Zinc deposits were made up on polished copper sheets using this bath and the following brightness data was obtained:

Current density (amps. per sq. ft.) 7 25 40 Not bright-dipped l0 9 14 17 Bright-dipped 17 26 27 29 A similar cyanide-zinc plating bath was made up including additionally eight grams per liter of molybdenum trioxide and with this modified bath specimen zinc electrodeposits were obtained with the following brilliance:

Current density The phenol-aldehyde condensation products illustrated in the above examples are used in about an optimum amount in each instance. It will be understood that this optimum was determined for each specific bath and addition agent by trying difierent amounts until an optimum was thus determined by trial and error. It will similarly be understood that any bath-soluble phenol-aldehyde condensation product may likewise be used in widely varying amounts and an optimum may be determined for each specific bath and proposed use by a few simple trials.

While the cyanide-zinc plating bath to which organic addition agents and metal brighteners are added in the examples is particularly well adapted to my purposes, it will be understood that any cyanide-zinc bath may be used. To obtain the best results it is desirable that the cyanide-zinc plating bath be as pure as possible. There are of course numerous other considerations as to cyanide-zinc plating bath composition already known to the art.

While I have shown numerous examples of zinc plating baths, it will be understood that one skilled in the art may readily prepare numerous baths containing bath-soluble, phenol-aldehyde condensation products with or without metal brighteners without departing from the spirit of my invention.

1 claim:

1. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyahide-zinc bath in the presence of a bath-soluble addition agent prepared by reacting materials consisting of a phenol and an aldehyde to produce a phenol-aldehyde condensation product.

2. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyanide-zinc bath in the presence of a bathsoluble addition agent prepared by reacting materials consisting of a phenol and an aldehyde to produce a phenol-aldehyde condensation prod- '4. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyanide-zinc bath in the presence of a bathsoluble phenol-aldehyde condensation product prepared by reacting materials consisting of, first, a phenol selected from the group consisting of cresol, catechol, hydroxydiphenyl, naphthol, and phenol with, second, an aldehyde selected from the group consisting of acetaldehyde, acetaldol, butyraldehyde, crotonaldehyde, formaldehyde, furfural, paraldehyde, and propionaldehyde.

. 5. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyanide-zinc bath in the presence of a bath-soluble phenol-aldehyde condensation product prepared by reacting materials consisting of, first, a phenol selected from the group consisting of catechol, cresol, hydroxydiphenyl, naphthol, and phenol with, second, an aldehyde selected from the group consisting of acetaldehyde, acetaldol, butyraldehyde, crotonaldehyde, formaldehyde, furfural, paraldehyde, and propionaldehyde, and a soluble compound of a metal of the group consisting of molybdenum, chromium, cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

6. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyanide-zinc bath in the presence of a bathsoluble phenol-aldehyde condensation product prepared by reacting materials consisting of, first, a phenol selected from the group consisting of catechol, cresol, hydroxydiphenyl, naphthol, and phenol with, second, an aldehyde selected from the group consisting of acetaldehyde, acetaldol, butyraldehyde, crotonaldehyde, formaldehyde, furfural, paraldehyde, and propionaldehyde, and a soluble molybdenum compound.

7. A cyanide-zinc plating composition containing a bath-soluble addition agent prepared by reacting materials consisting of a phenol and an aldehyde to produce a phenol-aldehyde condensation product.

8'. A cyanide-zinc plating composition containing a bath-soluble addition agent prepared by reacting materials consisting of a phenol and an aldehyde to produce a phenol-aldehyde condensation product and a soluble compound of a metal of the group consisting of molybdenum,-

consisting of, first, a phenol selected from the group consisting of catechol, cresol, hydroxydiphenyl, naphthol, and phenol with, second, an aldehyde selected from the group consisting of acetaldehyde, acetaldol, .butyraldehyde, crotonaldehyde, formaldehyde, furfural, paraldehyde, and propionaldehyde.

11. A cyanide-zinc plating composition containing a bath-soluble phenol-aldehyde condensation product prepared by re'acting materials consisting of, first, a phenol selected from the group consisting of catechol, cresol, hydroxydiphenyl, naphthol, and phenol with, second, an aldehyde selected from the group consisting of acetaldehyde, acetaldol, butyraldehyde, crotonaldehyde, formaldehyde, furfural, paraldehyde, and propionaldehyde, and a soluble compound of a metal of the group consisting of molybdenum, chromium, cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

12. A cyanide-zinc plating composition containing a bath-soluble phenol-aldehyde condensation product prepared by reacting materials consisting of first, a phenol selected from the group consisting of catechol, cresol, hydroxydiphenyl, naphthol, and phenol with, second, an aldehyde selected from the group consisting of acetaldehyde, acetaldol, butyraldehyde, crotonaldehyde, formaldehyde, furfural, paraldehyde, and propionaldehyde, and a soluble molybdenum compound.

RAYMOND A. HOFFMAN. 

